Oxygen Conductivity Research Articles

Materials AIILnInO4 with Ruddlesden-Popper Structure for Electrochemical Applications: Relationship between Ion (Oxygen-Ion, Proton) Conductivity, Water Uptake, and Structural Changes.

In this paper, the review of the new class of ionic conductors was made. For the last several years, the layered perovskites with Ruddlesden-Popper structure AIILnInO4 attracted attention from the point of view of possibility of the realization of ionic transport. The materials based on Ba(Sr)La(Nd)InO4 and the various doped compositions were investigated as oxygen-ion and proton conductors. It was found that doped and undoped layered perovskites BaNdInO4, SrLaInO4, and BaLaInO4 demonstrate mixed hole-ionic nature of conductivity in dry air. Acceptor and donor doping leads to a significant increase (up to ~1.5–2 orders of magnitude) of conductivity. One of the most conductive compositions BaNd0.9Ca0.1InO3.95 demonstrates the conductivity value of 5 × 10−4 S/cm at 500 °C under dry air. The proton conductivity is realized under humid air at low (<500 °C) temperatures. The highest values of proton conductivity are attributed to the compositions BaNd0.9Ca0.1InO3.95 and Ba1.1La0.9InO3.95 (7.6 × 10−6 and 3.2 × 10−6 S/cm correspondingly at the 350 °C under wet air). The proton concentration is not correlated with the concentration of oxygen defects in the structure and it increases with an increase in the unit cell volume. The highest proton conductivity (with 95−98% of proton transport below 400 °C) for the materials based on BaLaInO4 was demonstrated by the compositions with dopant content no more that 0.1 mol. The layered perovskites AIILnInO4 are novel and prospective class of functional materials which can be used in the different electrochemical devices in the near future.

Grain boundary energies in yttria‐stabilized zirconia

AbstractThe three‐dimensional microstructure of 8% yttria‐stabilized zirconia (YSZ) was measured by electron backscatter diffraction and focused ion beam serial sectioning. The relative grain boundary energies as a function of all five crystallographic grain boundary parameters were determined based on the assumption of thermodynamic equilibrium at the internal triple junctions. Grain boundaries with (100) orientations have low energies compared to boundaries of other orientations, and all [100] twist boundaries have relatively low energies. Other classes of boundaries with lower than average energies include [100] symmetric tilt boundaries with disorientations less than 40° and [111] twist boundaries with disorientations greater than 20°. At fixed misorientations, the relative areas of boundaries are inversely correlated to the relative grain boundary energy. The results suggest that texturing microstructures to increase the relative areas of [100] twist boundaries might increase the oxygen ion conductivity of YSZ ceramics.

Study of oxygen-ion conductivity and luminescence in the ZrO2 – Nd2O3 system: Impact of local heterogeneity

Stabilized fluorites and pyrochlores with different types of substitution in the (Nd2O3 − ZrO2 system (NdZrO)) have been studied by Raman spectroscopy, X-ray diffraction, and impedance spectroscopy methods. Ionic and proton conductivity maps for 9 compositions in the NdZrO system are presented. Oxygen partial pressure measurements show a typical ionic conductor behavior, with a significantly increase of conductivity for (Nd2−xZrx)Zr2O7+x/2 (x = 1.27) fluorite and (Nd2−xZrx)Zr2O7+x/2 (x = 0.4, 0.2) pyrochlores. For the same compositions the strong luminescence was observed. Strong luminescence and high oxygen-ion conductivity of these solid solutions can be associated with the presence of phases with the different degree of structural disorder (tetragonal phase, fluorite) in local nanodomains in fluorite or pyrochlore matrix in the ZrO2 − Nd2Zr2O7 region. Really, Raman spectra of (Nd2−xZrx)Zr2O7+x/2 (x = 0.5 − 0.2) solid solutions demonstrated the fluorite + pyrochlore structural type in the short-range order. Fluorite nanodomains in pyrochlore matrix (ZrO2 – Nd2Zr2O7 region) resulting from an order–disorder transition can only be detected at a radiation wavelength comparable to the fluorite nanodomain size. Thus, using Raman spectroscopy the broad isomorphism range in the ZrO2 – Nd2Zr2O7 system has been shown to be nonuniform.

Mixed Oxygen Ionic and Electronic Conducting Membrane Reactors for Pure Chemicals Production

AbstractTraditional gas separation technologies to produce pure oxygen, hydrogen and highly concentrated nitrogen, such as pressure swing adsorption and cryogenic separation, are cost and energy intensive. The mixed oxygen ionic and electronic conductor (MIEC) membrane can separate oxygen with 100 % selectivity, which can be applied as a platform reactor for pure chemicals production. In the MIEC membrane reactor, pure O2 can be directly produced. When the oxygen is all removed, highly concentrated N2 is generated. Moreover, if the feeding gas is water steam, hydrogen can be yielded through water decomposition. Significant progress has been made in the MIEC membrane reactor for pure chemicals production over the past few years. Therefore, this work summarizes the relative efforts on MIEC membranes for oxygen, nitrogen, and hydrogen purification. The principles of materials selection, membrane morphology optimizing, and reactions coupling are discussed in detail.

Sub-second sintering process for La6Sr4Co2Fe8O3-δ-gadolinium doped ceria composite cathode via a flash light irradiation method for intermediate temperature-solid oxide fuel cells

A solid oxide fuel cell (SOFC) requires an elevated operating temperature to achieve high oxygen ion conductivity and the oxygen reduction reaction (ORR). However, at high operating temperatures above 800 °C, performance deteriorates due to the chemical reaction of the electrode and electrolyte materials at the interface. Therefore, it is necessary to lower the operating temperature to the intermediate temperature regime while maintaining the high oxygen reduction reaction kinetics. One approach is adopting the composite cathode material such as La6Sr4Co2Fe8O3-δ-gadolinium doped ceria (LSCF-GDC). However, the high temperature in the fabrication process results in non-conduction material of strontium zirconate (SrZrO3, SZO) layers at the cathode/electrolyte interface, which blocks oxygen ion conduction and degrades the fuel cell performance. By utilizing the novel flash light sintering process, which can be completed in a few seconds, high temperature fabrication issues are solved. The surface microstructure and thickness of the composite electrode are inspected using a scanning electron microscope (FE-SEM). The secondary phase generation and chemical reaction are analyzed using XRD (X-ray diffraction), SEM-EDS, and TEM-EDS. The anode supported LSCF-GDC cathode cells are measured from 600 °C to 750 °C. The maximum power density at 750 °C of the novel flash light sintered LSCF-GDC composite cathode cell is 727.4 mW/cm2. In addition to the utilization of high performing cathode structure, the flash light sintering process dramatically reduces the process time and suppresses the side reaction at the cathode/electrolyte interface.

Scandium-doped barium ceria ferrites-based composite mixed conducting hollow fiber membranes for H2 and O2 permeation

BaCeO3-based ceramics are a unique class of perovskites that exhibit protonic and oxygen ionic conduction, which are ideal for high temperature hydrogen separation applications. This work features Sc-doped BCFe composites with nominal composition of BaCe0.70Fe0.30-xScxO3−δ (BCFSc) (x = 0, 0.05, 0.1, 0.15, and 0.2) that exhibit enhanced thermal, chemical, and mechanical stability. The BCFSc20 (x = 0.20) hollow fiber membranes demonstrated the highest hydrogen and oxygen fluxes among the Sc-doped composites of up to 0.32 and 0.20 mL min−1 cm−2, respectively, at 1000 °C. The BCFSc20 hollow fibers also displayed excellent stability under the hydrogen and oxygen permeation environments, while the permeation performance of the other BCFSc samples with low Sc content gradually deteriorated over the 120-h stability test.

Migration Kinetics of Surface Ions in Oxygen-Deficient Perovskite During Topotactic Transitions.

Oxygen diffusivity and surface exchange kinetics underpin the ionic, electronic, and catalytic functionalities of complex multivalent oxides. Towards understanding and controlling the kinetics of oxygen transport in emerging technologies, it is highly desirable to reveal the underlying lattice dynamics and ionic activities related to oxygen variation. In this study, the evolution of oxygen content is identified in real-time during the progress of a topotactic phase transition in La0.7 Sr0.3 MnO3-δ epitaxial thin films, both at the surface and throughout the bulk. Using polarized neutron reflectometry, a quantitative depth profile of the oxygen content gradient is achieved, which, alongside atomic-resolution scanning transmission electron microscopy, uniquely reveals the formation of a novel structural phase near the surface. Surface-sensitive X-ray spectroscopies further confirm a significant change of the electronic structure accompanying the transition. The anisotropic features of this novel phase enable a distinct oxygen diffusion pathway in contrast to conventional observation of oxygen motion at moderate temperatures. The results provide insights furthering the design of solid oxygen ion conductors within the framework of topotactic phase transitions.

Effect of varying Bi content on the temperature-dependent mechanical, dielectric, and structural properties of nominal Na1/2Bi1/2TiO3

Na1/2Bi1/2TiO3 (NBT) with varying Bi content has gained significant interest as a potential new material for solid-oxide fuel cells and oxygen separation membranes because of its excellent oxygen-ion conductivity. In this work, the effect of varying Bi content in NBT ceramics of compositions Na1/2BixTiO2.25+1.5x, where x = 0.485–0.510, on the temperature-dependent mechanical and dielectric properties and the crystal structure has been investigated, as these applications expose the components to high thermal and mechanical fields. The effects of Bi variation on phase compositions and structural transitions were systematically investigated by scanning electron microscopy-energy dispersive x-ray analyses and neutron diffraction at room temperature, in situ high-temperature x-ray diffraction, dielectric permittivity, and mechanical measurements. In-depth analysis of the temperature-dependent data shows that the Bi content of the samples does not alter the average crystal structure of the NBT; however, the temperature-dependent behavior of the latter depend on variations in Bi content and the associated oxygen vacancy concentration. This change in phase transition temperature displays a good correlation with the temperature-dependent ferroelastic response and with the Bi content.

Measuring Diffusion Coefficients of the Ceria Phase in a Dual-Phase Oxygen Permeation Membrane Using a Combined Polarization - Kelvin Probe Force Microscopy Method

Dual-phase membranes with FeCo2O4 or its iron-rich pendant Fe2CoO4 and Gd-doped ceria as an oxygen ion conductor have already been successfully applied as oxygen permeation membranes with high permeability in the temperature range above 800 °C [1-3]. Apart from Gd-doped ceria, Sm-doped ceria also can be an interesting alternative in this kind of composite due to its high ionic conductivity [4].As especially ceria or ceria-based composites have gained more and more interest for low-temperature applications, e.g. as catalyst materials, current research efforts are aiming to improve the composition and microstructure of such dual-phase membranes for application in a membrane reactor at considerably lower temperatures (below 600 °C) to perform partial oxidation reactions. For temperatures between 600-1200 °C the defect chemistry of these materials is well established, but experimental data for low temperature charge transport are limited and not fully understood, yet.Kelvin Probe Force Microscopy (KPFM) is an Atomic Force Microscopy (AFM)-based measurement method which can measure the local surface potential (or from the physics view: the Volta potential) of the sample [5, 6]. The surface potential is a measure for local changes of the defect chemistry, as it is directly related to the local Fermi niveau [7]. The implications of local oxidation and reduction at low temperatures for charge carrier mobility in pure ceria, and especially in dual-phase materials, are not very well understood so far, but KPFM can be used to measure the surface potential difference directly at the polarized contact area as well as to map the time-dependent relaxation process of the introduced gradient, also giving information about the local surface potential distribution, lateral extent of the gradient, variations of the shape of the gradient etc. [8, 9].In the present study, single ceria grains in a dual-phase Ce0.8Sm0.2O2-δ + FeCo2O4 oxygen permeation membrane were polarized at room temperature in ambient air using a Pt-coated AFM tip and a large silver paste back contact. Subsequently, the introduced defect concentration gradient (which is visible as a gradient of the surface potential) and the relaxation process over time was monitored by KPFM.By comparing the measurement results to previously acquired data of single phase ceria samples with different doping concentrations and crystallinity, we were able to show that by this technique, chemical diffusion coefficients of a single phase in a composite material are accessible. Acknowledgements: The work was funded by the German Research Foundation - project #387282673. Literature: Ramasamy, M.; Baumann, S.; Palisaitis, J.; Schulze‐Küppers, F.; Balaguer, M.; Kim, D.; Meulenberg, W. A.; Mayer, J.; Bhave, R.; Guillon, O. J Amer Ceram Soc 2016, 99 (1), 349-355.Ramasamy, M.; Persoon, E. S.; Baumann, S.; Schroeder, M.; Schulze-Küppers, F.; Görtz, D.; Bhave, R.; Bram, M.; Meulenberg, W. A. Journal of membrane science 2017, 544, 278-286.Lin, Y.; Fang, S.; Su, D.; Brinkman, K. S.; Chen, F. Nature Comm 2015, 6 (1), 1-9.Mori, T.; Drennan, J.; Lee, J.-H.; Li, J.-G.; Ikegami, T. Solid State Ionics 2002, 154-155, 461-466.Örnek, C.; Leygraf, C.; Pan, J. Corr Eng Sci Tech 2019, 54 (3), 185-198.Melitz, W.; Shen, J.; Kummel, A. C.; Lee, S. Surf Sci Rep 2011, 66 (1), 1-27.Zhang, Z.; Yates, J. T. Chem Rev 2012, 112 (10), 5520-5551.Neuhaus, K.; Schulze-Küppers, F.; Baumann, S.; Ulbrich, G.; Lerch, M.; Wiemhöfer, H.-D. Solid State Ionics 2016, 288, 325-330.Lee, W.; Lee, M.; Kim, Y.-B.; Prinz, F. B. Nanotechnology 2009, 20 (44), 445706.

Importance of Solid-Liquid Interface on Electrochemical Performance of Doped Ceria-Carbonate Composite Electrolyte for High Temperature Fuel Cells

Samaria-doped ceria (SDC)/carbonate composite electrolytes were recently developed for high temperature fuel cell applications. Conventional LiAlO2 was replaced by SDC as the matrix phase and lithium/sodium carbonate was selected as the second phase. In this study, the porous SDC (Sm0.2Ce0.8O1.9; SDC) matrix was fabricated. Then, the molten lithium sodium carbonate ((Li0.52Na0.48)2CO3; LNC) is infiltrated to form a composite electrolyte.From the cell testing in this study, the SDC/LNC cell show higher power density (340mW/cm2) than LiAlO2/LNC cell (154mW/cm2) at 650°C. This result suggests that the SDC-LNC composite electrolyte may be a better electrolyte for high temperature applications. In addition, the effects of solid-liquid interface was investigated using matrix with various pore sizes ranging from 5 to 20 μm. When the pore size of structural matrix was changed from 20 to 5 μm, the power density measured increased from 126 to 340mW/cm2 at 650oC. This can be attributed to the small pores having higher interface area, and the increased interface area is effective for transportation of ions. In other words, the super-ionic conducting path may exist at this interface, where the defect concentrations are high.Through the results and calculations of the designed experiments, the importance of the interface is realized. Finally, it may be concluded that the interface was mainly contributed by oxygen ion conduction using DC measurement under the control of different atmospheres and TEM analysis. High-resolution SEM, XRD, and Electrochemical Impedance Spectroscopy were employed to conduct microstructural, structural and impedance analyses.

Measurement of Polarization Resistances of LSCF/YSZ/LSCF Symmetrical Cell Using Alternating Current (AC) and Direct Current (DC) Techniques

Solid oxide fuel cells (SOFCs) are electrochemical devices, which can efficiently convert the chemical energy stored in fuels such as CH4 and H2 to electrical energy. SOFCs are of great significance for the next generation of clean energy storage and conversion. Yttria stabilized zirconia (YSZ) is a common solid oxide electrolyte used in SOFCs since it has outstanding oxygen ion conductivity, especially when operated at a high temperature (>800°C). Lanthanum strontium cobalt iron oxide (LSCF) is a mixed ionic-electronic conductor (MIEC), which offers both good electronic conductivity and good oxygen ion conductivity. Electrochemical impedance spectroscopy (EIS) is typically used to study the electrochemical performance of SOFCs. However, when using the common two-electrode EIS, the electrode processes at the cathode and anode cannot be studied separately. To study the electrode processes at the cathode and anode, a three-electrode EIS (two-electrode EIS with one pseudo-reference electrode) was performed on an LSCF/YSZ/LSCF bar-shaped symmetrical cell with platinum strip electrodes as probes. The point-by-point sum of the EIS spectra across the cathode and probe and across the anode and probe was found to match the impedance across the cathode and the anode. Also, polarity was switched, and it was found that the two electrodes do not necessarily have identical polarization resistance. Direct current (DC) measurements were also used to measure the polarization resistance of two electrodes separately with good agreement with the EIS results.

Boosting Proton-Conducting Ceramic Electrochemical Performance Through Mixed Ionic and Electronic Conducting Cathode Functional Layers

Proton conducting ceramic fuel cells (PCFCs) are a promising new technology for clean energy generation and green fuels production. PCFCs show favorable performance, but still lag behind their higher-temperature solid-oxide fuel cell predecessors. This work sets out to tailor the cathode-electrolyte interface in PCFCs by increasing the oxygen reduction reaction (ORR) activity and oxygen transference to bolster electrochemical performance and durability.The cathode-electrolyte interface is a major source of voltage loss during PCFC operation and is also suspected to be a primary contributor to cell-level degradation. Both oxygen reduction (ORR) and H2O formation must be simultaneously facilitated in PCFC cathodes. This contrasts with SOFC cathodes, where only oxygen reduction is required since water formation occurs separately at the anode. The dual reaction processes occurring in PCFC cathodes can lead to competitive interference between water adsorption/desorption and ORR activity. We hypothesize that placing materials with high ORR activity and oxygen-ion conduction at the electrolyte-cathode interface may help alleviate polarization loss.To explore this hypothesis, Er0.4Bi1.6O3 (ESB), Dy0.08W0.04Bi0.88O1.56 (DWSB), Gd0.1Ce0.9O1.95 (GDC10) and SmCoO3 were fabricated into the cathode functional layers (CFLs) in this study. As the addition of an interlayer to the cathode-electrolyte interface can inadvertently effect the morphology (e.g. roughness, porosity) and mechanical integrity of the interface, control cells with a porous BaCe0.4Zr0.4Y0.1Yb0.1O3- δ BCZYYb cathode functional layer were also fabricated and tested. Button cells with the CFLs were fabricated through ultrasonic spray coating of thin layers of the CFL material onto a precursor BCZYYb electrolyte and co-fired. The cathode is then brush painted onto the resulting half-cell and sintered. Preliminary results, shown in Figure 1a, demonstrate that adding an ESB CFL can increase performance by over 40%. While GDC-based CFLs have led to significant increases in PCFC durability, displayed in Figure 1b, underscoring the promise of this technique. Figure 1

Microscopy Studies of the Novel Fluorinated Ionomers for Proton Exchange Membrane Fuel Cells

Perfluorosulfonic acid (PFSA) ionomers, such as Nafion, are widely used as a thin film on the Pt/C surface in the catalyst layers (CLs) in PEMFCs. They consist of polytetrafluoroethylene (PTFE) backbones and hydrophilic sulfonic acid group side-chains that facilitate the proton transport to the active sites in CLs. However, due to poor oxygen permeation through Nafion in CLs a new design of oxygen-permeable ionomers is required. In this regard, novel ionomers are synthesized by copolymerization of perfluoro-2,2-dimethyl-1,3-dioxole (PDD) with perfluoro(4-methyl-3,6-dioxaoct-7-ene) sulfonyl fluoride (PFSVE) and a ter-monomer. PDD and PSEPVE are providing improved oxygen permeability and ionic conductivity, respectively. PDD cathodes not only showed higher performance at high current densities than Nafion, but also better durability. In this work, the effect of the PDD content on the morphology and structures of the catalyst layer, before and after accelerated stress testing, was investigated through comprehensive characterization approaches. The PDD membrane electrode assemblies (MEAs) showed less catalyst layer thinning after 30K SWAST compared to Nafion. In contrast, PDD CLs displayed a considerable number of lateral cracks non-uniformly distributed, compared to the Nafion CLs, which could be due to the PDD’s different wetting properties during sample preparation. High PDD content in the CLs (62-68 mole%) resulted in the highest total porosity loss and Pt/Co change than low PDD content (24-36%), which was reflected in its highest performance loss among all the PDD MEAs. PDD cathodes also displayed lower particle size growth, lower Co loss, a lower degree of ionomer changes. In this talk we will discuss our characterization approach to determine a number of structural and compositional parameters, and correlate those findings with the performance and durability.

Effect of fuel choice on conductivity and morphological properties of samarium doped ceria electrolytes for IT-SOFC.

The present investigation is emphasized on the effect of various combustion agents on the crystal properties, surface microstructure, and oxygen ion conductivity of 20% mole-Sm doped ceria (Ce0.80Sm0.20O1.90/SDC20) ceramics as solid electrolyte for IT-SOFCs. The most widely used combustion agents for engineering ceramic production as ethylene glycol, diethylene glycol, triethylene glycol, L-alanine, L-valine, glycine, citric acid monohydrate, urea, and EDTA-citric acid were compared in terms of SDC20 properties. X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and electrochemical impedance spectroscopy (EIS) were used to determine the microstructure properties, crystal structure and ionic conductivity of SDC20 powder. XRD pattern of the ceramics revealed the formation of single-phase fluorite structure. According to the results of electrochemical analysis, the maximum total ionic conductivity was observed in SDC20 electrolyte synthesized using triethylene glycol as the fuel among all the synthesized electrolytes (5.72 x 10–2 S.cm–1).

Enhanced Electrochemical Performance and Durability of the BaCo0.4Fe0.4Zr0.1Y0.1O3−δ Composite Cathode of Protonic Ceramic Fuel Cells via Forming Nickel Oxide Nanoparticles

In protonic ceramic fuel cells (PCFCs), oxygen reduction reaction activity is governed by the oxygen adsorption/dissociation, proton conduction, and electron transfer kinetics. Although various strategies have been explored to enhance the proton and electron conductivity via tuning the oxygen vacancy concentration in the electrode materials and introducing electronic conducting agents, there are few studies on improving oxygen adsorption/dissociation (surface-exchange reaction) kinetics in PCFCs. In this study, we report uniformly distributed thermodynamically stable nickel oxide (NiO) nanoparticles as a catalyst to enhance the electrochemical performance of the BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) cathode, which is a promising cathode material because of its triple (oxygen ion, proton, and electron) conductivity in PCFCs, by improving surface-exchange reaction kinetics. The 0D NiO nanoparticles with high adsorption and fast dissociation ability of oxygen could enlarge the active sites for surface-exchange reactions without fading the BCFZY surface and triple-phase boundaries where the H2O formation reaction occurs. The cathode employing NiO nanoparticles exhibits largely reduced polarization resistance and a superior power density of 780 mW/cm2 at 600 °C. This improvement is attributed to the enhanced surface-exchange reaction kinetics.

Evolution of Sm‐Doped Fe2O3/CeO2 Oxygen Carriers in Chemical Looping Hydrogen Generation

The Sm‐doped Fe2O3/CeO2 is desirable for chemical looping hydrogen generation (CLHG) owing to its satisfactory oxygen ion conductivity, and the reactivity of Fe2O3/Ce0.8Sm0.2O1.9 (FSDC20) is the highest among the Sm‐doped Fe2O3/CeO2 oxygen carriers with different Sm‐doping amounts. This work is focused on the performance evolution of FSDC20 in CLHG with Fe2O3/CeO2 (FSDC0) as comparison, and the related mechanisms are explored. The results show that the evolution of H2 yield with redox cycles for both samples contain an activation and an attenuation process, and the fourth cycle acts as the demarcation point for FSDC20 before the H2 yield stabilizes. Specifically, the activation mainly lie in the phase transition from Fe3O4 to FeO, and the activation and attenuation processes can be ascribed to the particle microstructure evolution. For the activation process in the first four cycles, the grains on the particle aggregate together, however, with porous structure, and the improved reactivity can be attributed to the enhanced interaction between Fe2O3 and CeO2 as well as the generation of CeFeO3. However, the grains continue to aggregate on a large scale after the fourth cycle, leading to serious sintering and thus the attenuation process.

Evolution of oxygen reduction property by the role of CeO2 in CeO2/MnO2 cathode catalyst for passive direct methanol fuel cells

The oxygen reduction reaction (ORR) efficiency of direct methanol fuel cell (DMFC) is of great significance. In this work, MnO2 supported on CeO2-QDs (CeO2-QDs@MnO2) and CeO2-QDs supported on MnO2 (MnO2@CeO2-QDs) composite with different loading method were synthesized to investigate the role of CeO2 for ORR, according to the excellent oxygen adsorption and oxygen ion conductivity of CeO2 quantum dots (CeO2-QDs). A passive DMFC was assembled by CeO2-QDs@MnO2 or MnO2@CeO2-QDs as cathodic catalyst and PtRu/C as anodic catalyst. The maximum power densities for CeO2-QDs@MnO2 and MnO2@CeO2-QDs-based DMFCs were 9.4 and 7.8 mW·cm−2, while 8.5 and 7.0 mW·cm−2 for air-breathing DMFCs, respectively. CeO2-QDs@MnO2 showed a more superior ORR activity and stability in the high discharge currents especially for air-breathing DMFCs. The temporary storage and timely replenishment mechanism of oxygen in CeO2-QDs@MnO2 catalyst could significantly enhance the ORR efficiency at cathode. This work developed a new thought about the loading method of CeO2 on the ORR catalytic activity for CeO2/MnO2 catalysts.

ТЕРМОДИНАМИЧЕСКАЯ ОЦЕНКА УСТОЙЧИВОСТИ ОКСИДНЫХ СИСТЕМ ПРИМЕНИТЕЛЬНО К МАТЕРИАЛАМ ДАТЧИКА КОНТРОЛЯ КИСЛОРОДА В НАТРИИ

The oxygen content in liquid sodium is an important normalized parameter that must be controlled during the operation of reactor fasilities with a sodium coolant. When developing a means of monitoring oxygen in liquid sodium, a careful selection of materials from which the sensitive elements of the control device (sensor) will be made is necessary. The criteria for selecting the sensor material include: acceptable corrosion resistance in liquid sodium under operating conditions; sufficient conductivity of oxygen ions at operating temperatures to generate a useful signal; and satisfactory resistance to thermal shock. Thermodynamic analysis allows to select materials that are potentially corrosion resistant to sodium in the sensitive element of the oxygen control sensor. The article presents a thermodynamic analysis of some metal oxide systems in contact with the sodium heat carrier of a sealed non-isothermal circulation circuit and an analysis of the stability of oxide systems in liquid sodium, which are the basis of ceramic sensing elements. It is shown that under certain conditions, deoxidized sodium can partially reduce the oxides of ceramics based on zirconium and hafnium with the addition of oxides of certain lanthanides. In addition, sodium reduces silicon oxide, on the basis of which sitall is produced, which is a candidate material for sealing the sensor sensor element. The analysis is performed using diagrams in the “electromotive force - temperature” coordinates constructed from thermodynamic data.

A rational design of FeNi alloy nanoparticles and carbonate-decorated perovskite as a highly active and coke-resistant anode for solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are a kind of clean and efficient device to convert chemical energy in fuels into electricity. However, since anodes with high catalytic activity and carbon tolerance are still underdeveloped, the consequent serious performance degradation of the cells under operational conditions significantly confines their commercial applications. Here we propose a new strategy to remove carbon deposition by in-situ formation of alkali metal carbonate on the anode surface. A multi-phase composite anode, which is composed of an orthorhombic single perovskite main phase, a Ruddlesden-Popper (RP) layered perovskite second phase, and an in-situ exsolved FeNi alloy minor phase, is developed by one-step reduction of La0.65Li0.05Sr0.3Fe0.8Ni0.2O3-δ (LLSFN0.05) at a high temperature. The deficiencies of the RP phase and A-site caused by Li dopant would increase oxygen bulk diffusion, and FeNi nanoparticles would boost the catalytic activity. Moreover, when dealing with carbon fuel, lithium carbonate can be synthesized on the anode surface, serving as a good oxygen ion conductor and an efficient catalyst for coke removal by gasification. A single cell with our reduced LLSFN0.05 anode exhibited maximum power densities of 596, 467, and 424 mW cm−2 at 750 ℃ with H2, CO, and wet C2H6 as the fuel, respectively. In addition, the cells could have a long-term stable operation for over 80 h using CO as the fuel at 200 mA cm−2. This study provides a new material design strategy to develop a highly active and coke-resistant anode.

Structure, synthesis, properties and solid oxide electrolysis cells application of Ba(Ce, Zr)O3 based proton conducting materials

Ba(Ce, Zr)O3 based proton-conducting oxides have experienced a surge of attention in the past because of their promising applications in proton-conducting solid oxide electrolysis cells (H+-SOECs). As proton conductor perovskite oxides, Ba(Ce, Zr)O3 based materials demonstrate potential to offer lower activation energy and higher proton transfer properties in low-temperature than oxygen ion conductor perovskite oxides as a result of the smaller ion radius of proton. Herein, a review of the current research progress on Ba(Ce, Zr)O3 based materials, including structural, materials synthesis approaches, conductivity, stability properties, and applications related to H+-SOECs is presented. This review focuses on modification strategies, including enhancing conductivity and chemical stability via the substitution of the B-site element, to improve the performance of H+-SOECs. Finally, more attention should be given to current leakage, performance and long-term stability of H+-SOECs in the future.